The switching of logic circuits on densely integrated modules or chips gives rise to electrical noise in the form of transient current or voltage spikes that must be decoupled or damped. A conventional means for effecting decoupling is to use decoupling capacitors, either external to the circuit module or as a portion of the module.
Where a remote external capacitor is used, an inductive path is established which does not allow damping of the electrical noise. Though a discrete capacitance may be moved closer, it is not possible to place a capacitor on board in sufficiently close proximity to prevent voltage drop or noise. Not only do problems persist using these solutions, but the components that implement the practice tend to be both ineffective and larger than desirable. On chip capacitance is the ideal solution, but the inherently large space required for a capacitive element prevents optimum use of chip space or real estate, adding to chip complexity, which is a significant problem as ever higher circuit densities are sought.
It is also necessary to pass the signals on signal lines from the circuit module without permitting the escape of unwanted harmonics. It is vital that such unwanted signals be removed nearest the source and only the desired bandwidth of signals be transmitted from the module enclosure. Each signal line should be provided with a filtering capability adapted to cut off signals having a frequency that exceeds a designated bandwidth of frequencies on the line to reduce spurious signals or noise that may escape the shielded confinement of the circuit module package assembly.